This research involves laboratory studies of the development of aggression and predation in the grasshopper mouse, Onychomys torridus. This species is a carnivorous rodent showing highly developed prey- killing behavior and pronounced aggressive behavior toward individuals of its own species and other rodent species. It affords an ideal opportunity for descriptive and experimental analysis of the ontogeny of these behaviors. The particular focus of this study is to analyze parental influences on the ontogeny of predation and aggression by means of cross-fostering Onychomys and Peromyscus. The latter is a non-predatory, less aggressive genus with a number of biological similarities. Cross-fostering is used as one of several experimental techniques to study the role of early experiences and social influences in the development of various types of aggression and predation in this species. Studies on food hoarding and spontaneous seizures have also been undertaken. It is hoped that further work will show Onychomys as an interesting laboratory model for the study of animal epilepsy.